# [texhax] Q: bold variables in math mode

Donald Arseneau asnd at triumf.ca
Wed Jun 1 20:07:40 CEST 2011

"D. R. Evans" <doc.evans at gmail.com> writes:

> I need to be able to typeset something like:
>   A = CM
> in math mode where A and M are bold, but C is roman.
>
> As long as I don't redefine \bf, then the following works:
>   ${\bf A} = {\rm C} {\bf M}$
>
> But I have:
>   \font\bf=ec-lmbx12 at 10.5pt
> and now when I type the math mode expression, A, C and M are all rendered
> in math italic instead of bold.
>
> How do I get A and M to render in the bold face I am defining with the
> above \font\bf command?

You do not use a \font\bf command!  Instead do \show\bf to see how
the \bf font selection is already defined, then, assuming "\tenbf", do
\font\tenbf=ec-lmbx12 at 10.5pt
But this doesn't affect the math font assignment that has already been
done (\textfont\bffam=\tenbf) so you have to repeat that assignment:
\textfont\bffam=\tenbf
to apply the new tenbf.

This setting up fonts is all very fussy work in plain TeX and one of
the main reasons not to use plain TeX.  Why are you uding it?

Donald Arseneau                          asnd at triumf.ca